[gdal-dev] Odd problem -- Gdalwarp, OpenCL and interpolation

[Jonathan Williams]

To clarify: doing the gdalwarp resample without OpenCL is producing a
realistic Float32 value range. Doing it WITH OpenCL is producing far
higher values.

This is on a Tesla M2090. No other experiments/benchmarks have produced
this kind of result, and as I wrote below, gdalwarp itself works when
only doing reprojection, not resampling, regardless of whether OpenCL is
used.

Jonathan


On 3/5/2016 7:06 PM, Jonathan Williams wrote:
> Hello,
> I've run into an odd problem that I suspect is the result of some
> incorrect variable type casting, but I'm not sure where to look or how
> to fix it.
>
> Inputting a raster in Float32 format (or Float64, with -ot Float32
> and/or -wt Float32 enabled on the command line) and attempting to do a
> resample interpolation (doesn't seem to matter what OpenCL-compatible
> algorithm) is producing output that is huge compared with the input. The
> output still has a range of values, and it makes me wonder whether the
> output is being multiplied by a very large amount at some point.
>
> Saga GIS reports the non-OpenCL resampled Float32 values as ranging from
> -8.595017433166504 to 166.74661254882812, and the resampled values as
> ranging from -340282346638528860000000000000000000000 to
> 340282346638528860000000000000000000000 (+/- 3.4e38, e.g. the maximum
> range of single precision floating point)
>
> Running the exact same warp with OpenCL disabled produces the correct
> output.
>
> Here's an example of the gdalwarp runline:
>
> gdalwarp -srcnodata 9999 -dstnodata 9999 -wt Float32 -ot Float32
> --config GDAL_CACHEMAX 4096 -wm 2048 -multi -tr .03 .03 -r lanczos
> --debug on -overwrite -wo "USE_OPENCL=TRUE" 373.grib2 373_res.tif
>
> I will note that the input file in this case is in Float64 format;
> however, converting it to Float32 prior to the warp makes no difference.
> Neither does whether the input file is in grib2 format or geotiff format.
>
> Reprojection-only operations produce normal-looking output using OpenCL.
>
> Best,
> Jonathan
>
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